1. Field of the Invention
The present invention relates to a holder for a drive piston of a setting tool.
2. Description of the Prior Art
European Publication EP-O 346275 B1 discloses an explosive powder charge-operated setting tool including a piston guide and a drive piston displaceable in the piston guide. The piston guide has radial openings facing the drive piston, and spring-biased braking balls extending through the radial openings and engaging the drive piston. The spring, which applies a biasing force to the braking balls is formed as a ring spring for applying a radially acting, with respect to the piston, biasing force to the braking balls. The ring spring is provided on its inner profile with a bearing surface acting on the braking ball. The bearing surface is inclined to the piston at an acute angle that opens in a direction opposite a setting direction.
In an ignition-ready position of the drive piston, the braking balls engage the circumferential surface of the piston body of the drive piston. When the drive piston moves in the setting direction, it entrains therewith the braking balls, rolling them over. The braking balls expand the ring spring, which results in the bearing surface transmitting the radial biasing force to the braking balls. The braking balls are pressed radially against the piston body by the ring spring. Even with a small displacement of the drive piston in a direction opposite the setting direction, the braking effect can be substantially reduced or eliminated, as the braking balls displace in the same direction as the drive piston, unloading the ring spring. After being unloaded, the ring spring does not press any more the braking balls against the piston body. Further, a possibility still remains that the drive piston would be displaced, before ignition or firing of the setting tool, in the setting direction as a result of, e.g., the setting tool being pressed too hard against a constructional component. The displacement in the return direction is effected due to cooperation of the ring spring with the braking balls. Thereby, the drive piston is reliably retained in its ignition-ready position.
U.S. Pat. No. 4,162,033 discloses a setting tool with a braking element that continuously applies a braking force to the drive piston.
An object of the present invention is to provide a piston holder having a simplified design and which would reliably retain the drive piston in its ignition-ready position in the absence of ignition.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a piston holder including at least one clamp member that is constantly non-rigidly pressed against a circumference of the drive piston and elements for supporting the at least one clamp member for an eccentric movement in a plane in which a central axis of the drive piston is located. The piston holder according to the present invention is particularly suitable for braking or retaining a drive piston, e.g., of explosive powder charge-operated setting tool, though it can also be used in a setting tool driven upon ignition of an air-fuel mixture.
The basic idea of the present invention consists in providing at least one clamp member located sidewise of the drive piston and engaging the same, so that the drive piston entrains the at least one clamp member upon moving in a drive-out or setting direction of the drive piston as a result of frictional contract therebetween, with the clamp member being tilted or pivoted about a pivot point located eccentrically relative to the clamp member in such a way that it runs into the travel path of the drive piston. Because the clamp member is simultaneously pressed against the drive piston, the frictional forces between the clamp member and the drive piston increase, providing for braking of the drive piston. When the setting tool is fired or ignited, the drive piston-displacing force increases and when it exceeds a predetermined value, the clamp member releases the drive piston due to its elastic deflection, and the drive piston can slide through the piston guide. There is provided in this way a speed-dependent friction coefficient that insures reduction of friction in the contact point between the clamp member and the drive piston with the increase of the drive piston displacement speed. The non-rigid support of the clamp member serves practically as a overload protection means against complete stop of the drive piston based on the principle of self-powering of the clamping action.
Upon movement of the drive piston in a direction opposite to its drive-out or setting direction, it again entrains the clamp member that would pivot or tilt about its eccentric pivot point in the opposite direction. The clamp member, being pivoted in the opposite direction, would apply a smaller pressure to the drive piston so that the drive piston can move to its initial or ignition-ready position substantially friction-free. The drive piston is held in its ignition-ready position by the clamp member that is constantly spring-biased against the drive piston. That insures a reliable positioning of the drive piston in its ignition-ready position.
In principle, the clamp member is formed as a pendulum one end of which is pressed against the circumferential surface of the drive piston, and at the other end of which, there is provided a pivot point radially spaced from the drive piston and pressure-biased toward the drive piston. In the drive-out or setting direction of the drive piston, this pivot point lies in front of the contact point of the clamp member and the drive piston when the drive piston is in its ignition-ready position. Upon entrainment of the clamp member by the drive piston movable in its drive-out or setting direction, the friction force increases as a result of the pivotal or tilting movement of the clamp member until the clamp member engages a stop provided in front of the clamp member in the drive piston drive-out direction. After the clamp member engages the stop, the pivot point and the contact point of the clamp member with the drive piston lie one behind the other in the radial direction relative to the drive piston. Upon movement of the drive piston in the opposite direction, i.e., to its initial, ignition-ready position, the pendulum would rotate or pivot in opposite direction, releasing the drive piston.
According to one embodiment of the present invention, the clamp member is freely tiltably retained in a receiving space stationary with respect to the setting tool. Practically, the clamp member is loosely located in this space and is radially pressed against the drive piston.
The clamp member can be formed as a rigid body and be pressed against the drive piston by spring means. However, the clamp member can also be formed as an elastic body supported between the drive piston and a wall of the receiving space radially spaced from the drive piston.
According to the present invention, a plurality of clamp members can be uniformly distributed in a circumferential direction of the drive piston and be biased against the drive piston by a common ring spring.
In principle, the clamp member can have different shapes in the plane extending in the axial direction of the drive piston. It only needs to be insured that the contact point of the clamp member, at which the clamp member engages the drive piston, be capable of running into the travel path of the drive piston upon movement of the drive piston in its drive-out or setting direction.
According to a further embodiment, the clamp member pivots about an eccentric axle. The eccentric axle can be stationary arranged in the setting tool, and the clamp member can be formed as an elastic body. In this case also, the clamp member functions as a pendulum that runs into the travel path of the drive piston when it moves in its drive-out direction until the clamp member abuts a stop.
Alternatively, the excentric axle can be non-rigidly supported in the radial, with respect to the drive piston, direction, and the clamp member can be formed as a rigid body. In this case, self-clamping of the clamp member is prevented.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of the preferred embodiment, when read with reference to the accompanying drawings.